Continuous coating by immersion (called "freeze-coating" technique) involves a fast feeding of the workpiece through a vessel spout filled with molten coating material which solidifies on contact with the workpiece.
Several conventional processes and devices are based on this technique. Thus, for example, British Pat. No. 982,051 describes a process for coating very thin silica fibers with aluminum, consisting in advancing the fiber downwardly through a vertical slit provided at the extremity of a vessel spout or nozzle, molten aluminum being continuously supplied to the lateral edges of the slit by the intermediary of the nozzle in such manner as to become deposited on the fiber traversing the melt. Fibers so coated, upon emerging from the bath, may be surrounded by an atmosphere of low oxidizing effect designed to avoid the formation of an oxide pellicle on the resulting coating. However, a major disadvantage of this procedure lies in the fact that the downward movement of the fiber causes an irregular and too abundant outflow of the aluminum from the nozzle and makes it difficult to control the quality and the uniformity of the obtained coating. Such a process, moreover, appears to be almost exclusively limited to the deposition of aluminum layers since the utilization of another material, necessarily more fluid, would cause unavoidable leakage of the molten mass from the nozzle.
Another known process for the continuous coating of a steel strip with aluminum, described in French Pat. No. 1,584,626, resides in upwardly advancing, at a maximum velocity on the order of 10 meters per minute, the previously degreased and/or pickled steel strip through the slit of a heated supply nozzle of refractory material filled with molten aluminum, the speed of the strip being such that the residence time of the strip in the nozzle is between 0.03 and 1 second. However, this relatively long residence time only limits but does not completely avoid the formation of a fragile intermetallic layer at the steel/coating interface and causes also an annealing of the substrate. Such a process remains, furthermore, limited to the coating of strips of small thickness (maximum possible thickness on the order of 0.5 mm). Besides, the absence of a neutral atmosphere at the nozzle outlet creates problems regarding the centering of the coating on the strip.
There exist also a number of other processes and devices for coating strips or wires. However, the coating velocity obtained with all these processes or devices are limited, the maximum speed being in fact on the order of 10 meters/minute.